1. Field of the Invention
The invention relates generally to the construction of exterior windows suitable for use in commercial or residential buildings. In particular, the invention relates to a latching mechanism for window sashes that allows the sashes to withstand high forces, such as the wind forces that occur during storms.
2. Background Information
Exterior windows are designed to provide a weather-tight barrier against the elements. During most weather conditions, windows are subject to only nominal forces. These forces can easily be withstood by conventional window designs. Yet, during severe weather, exterior windows may be subject to much greater forces. A category 1 hurricane, the least severe type according to the Saffir-Simpson scale, produces winds in excess of 74 mph. A category 4 hurricane, a more severe type, can produce winds up to 155 mph. Similarly, a mild category F-0 tornado (according to the Fujita scale), produces winds of up to 72 mph, while more powerful tornadoes can generate winds of 260 mph or more.
High speed winds may exert large forces against an exterior window. The magnitude of a wind force is proportional to the square of the wind speed, causing wind force to increase rapidly as wind speed increases. Wind typically exerts two types of force on an exterior window. The first type, a sustained force, is an almost constant force that may last, for example, up to a minute or more. The second type, an intermittent force, is a momentary force created by a higher-speed wind gust and may last up to a few seconds.
Sustained and intermittent forces are often exerted upon exterior windows in multiple directions. Generally, wind blowing against a building creates a positive force (an inward force) on the windward side of the building and a negative force (an outward or suction force) on the leeward side of the building. Depending on the shape of the building, negative forces may also be exerted on walls parallel to the wind. As wind direction shifts, placement of positive and negative forces constantly changes.
Conventional window designs are often ill suited to withstand the severe forces created by hurricanes and tornadoes. While glass breakage is the most common mode of failure, window sashes and frames themselves may fail under force. When a window is subject to extreme forces, a window sash may dislodge from the window jamb. This problem is particularly acute in double-hung windows where the sash travels in a track or channel, and is not attached to the jamb by hinges or other fasteners. Once dislodged from the jamb, a sash may be blown into, or out of, the building, potentially injuring occupants of the building or passersby. Further, wind and water may enter the building through the window opening, damaging the building and its contents.
Latching mechanisms have been designed that purport to better secure window sashes to their jambs. Some of these latching mechanisms employ a bolt device that extends into the window jamb. While providing some benefit, these previous designs have suffered from poor performance. Under high forces, the prior latching mechanisms have tended to lift and separate from sashes, often allowing their bolts to break free and dislodge. When this occurs, the sash may be blown from the jamb despite the latching mechanism.
What is needed is an improved window sash latch that more effectively secures a window sash to a window jamb than the prior designs. Such a window sash latch should better withstand forces incident upon the window sash, and demonstrate superior resistance to separation from the sash. An improved window sash latch must also be easy to operate and relatively inexpensive to manufacture.